Shaft guard for lawn mowers



June 14, 1960 cs. w. STAHL 2,940,241

SHAFT GUARD FUR LAWN MOWERS Filed Sept. 15, 1958 Nif/6 INVENTOR. G/enn w. Stahl i) Anon/@ 2,940,2414 sHAFr GUARD lFOR LAWN MowERs Glenn W. Stahl, Kingsville, Mo., assignor to Keen Manufacturing Co., Inc., Kansas City, Mo., a corporation of Missouri Filed sept. 1s, 195s, ser. No. 160,838

7 claims. (ci. slt-25A) The present invention has to do with lawn mower improvements and more particularly, to the elimination of problems incident to damage of the drive shaft of an engine to which the cutter blade of the mower is attached.

Lawn mowers of the type in which a rotary blade is mounted for horizontal rotation beneath a mobile platform, are inherently subject to damage which oftentimes becomes excessive whenever the blade strikes objects such as heavy rocks, fences, trees and the like with a resultant sudden stopping of the rotation of the blade. Attempts heretofore made to solve the problem include the scr-called clutch attachment of the blade to the engine shaft so that theoretically, the shaft continues to rotate if the blade srikes a nonyieldingnobject. The fallacy of such reasoning becomes apparent however, when it is realized that the shock is so sudden that damage occurs particularly to the drive shaft before any such relative rotation of the shaft to the blade can possibly occur.

Consequently, the shafts are deliected out of true and bent, oftentimes at rather sharp angles, necessitating costly repair and replacement.

lt is, therefore, the most important object of the present invention to provide a guardfor the drive shaft of a lawn mower for preventing undue deflection as the result of the cutter blade striking various objects, which guard is easily attached to virtually any type of mower of this character and universally adapted for standard shafts commonly employed therein.

Another important object of the instant invention is to provide a guardthat, in addition to limitingthe extent of lateral deection of the shaft, permits the latter to flex slightly under the influence of the shock to the end that forces of the initial impact are absorbed, thereby lessening consequent'damage to other parts of the mower, including the engine itself. Y

In the drawing:

Fig. 1 is a fragmentary, vertical, cross-sectional view through a lawn-mower having a shaft guard made pur` ysuant to the present invention and taken on line 1-1 of Fig. 2;

Fig. 2 is a fragmentary, inverted view looking upwardly toward the shaft guard and proximal parts of the lawn mower wherein parts are broken away and shown in section; and

Fig. 3 is a fragmentary, side elevational view of the lawn mower on a reduced scale and having a portion of the platform thereof broken away and parts shown in section to illustrate the shaft guard.

The lawn mower chosen for illustration of the principles of the instant invention is of conventional character in that it is provided with a hollow, downwardly-facing platform 12 rendered mobile through use of a plurality of ground-engaging wheels 14.

An engine 16 carried by the platform 12 thereabove has a vertical drive shaft 18 extending through the platform 12 and depending therebelow to which is attached a cutter blade 20 for rotation within a substantially horizontal plane. Guard 22 forming the subject matter of nite States YlDatent the instant invention and designed to protect the shaft 18, loosely surrounds the latter in coaxial 'relationship thereto. To this end, therefore, a preferred construction is, Vas illustrated in the drawing,whereinguard 22 isgin-ilthe nature of a hollow, cup-shaped or substantially frustoL conical` body having a support-portion 23, anda flat bottom 24 in parallelism with the platformy 12 andthe blade 29. 4It is within such flat bottom portion 24 of the guard 22 that a circular opening 26 is formed for loosely receiving the shaft 18 just above the blade 20, but in close juxtaposition thereto and spaced below the bottom of the platform 12. Thus, as best seen in Fig. 1, it is to be preferred that the bottom 24 and, therefore, its opening 26, be next adjacent nut flange or stop 28 commonlyemployed to limit the extent of upward movement of the blade 20 along shaft 18. Y Y

Guard 22 is attached directly to the platform 12 and to this end, it is provided with an integral, outturned, annular flange 39 at its uppermost edge which bears flatly against the lower face of lthe platform 12. It is advanf tageous to provide common means of attachment for engine 16 and guard 22 to the platform 12 and, therefore, fasteners such as engine mounting bolts m32,- pass through platform 12 and through the flange 30 as is clear inthe drawing. A recess 34 in guard 22, defined in part by a. reinforcing upstanding, arcuate wall 36, clears o il drain plug 38 for engine 16 by virtue of an opening 40 in guard 22. y

When the lawn mower 1G is placed in normal use., guard 22 has no adverse effect upon the freedom of the cutting action since, as is well known, the cutting action occurs only rat the tips of the blade 20 radially remote from the axis of the shaft 18. j Furthermore, guard A22 will not interfere with discharge of. the cuttingsg/in fact, its relatively smoottnconical, outer surface will tend to deflect the cuttings downwardly away from the bottom of the platform 12 and tend Ito eliminate winding about the shaft 18 or clogging. and collecting in and aroundthe platform 12. Y f

In the event, however, that the blade 20 comes into Contact with objects that stop or tendvto stop the rotation thereof, undue lateral deflection of shaft 18 is prevented because of shaft 1S engagingthe circular edgeof guard 22 forming the opening 26 in the bottom 24 there- The materials from which drive shafts 18 for engines 16 are normally made, have a certain degree of resiliency, notwithstanding the hardness thereof. If, however, the shaft'is unduly deflected, it will set up a bend therein, necessitating repair or replacement.

By Way of example only, for a M3 inch diameter shaft of standard manufacture it has been found that the diameter of opening 26 should be 1%; of an inch. when the 'axial distance along the shaft between the periphery of'an opening 26 and the shaft bearing is approximately 2% inches.

The clearance between the shaft and the guard opening periphery allows limited lateral shaft deection which prevents the shaft from bending or setting up under impact. That is, it permits shaft deflection within the limit of resilient shaft flexure.

Noteworthy is the fact that the guard 22, because of its peculiar shape and coniigurationhis adequately able to withstand the shock of impact of the shaft 18 thereon in any direction, the forces being dissipated evenly in an outward direction toward the flange 30 and, therefore, platform 12.

The provision of the clearance in opening 26 around the shaft 18 so that no part of the guard 22 actually contacts shaft lduring normal use, is highly important, not only from the standpoint of eliminating all frictional resistance to free rotation of shaft 18, but more important, to permit shaft 18 to deflect and yield slightly in response to'thefirnpact and thereby reduce damage to blade 20, as

`well asi-to the bearings and other parts of the engine 16 whenever the Vrotation of blade 20.1's retarded or suddenly thelawnmower 10.51."V Y .v g Y l respect, -the fusego'f bearings, bushingsorthelike e shaft and in engagement therewith, is, to be Vstopped* because of striking jheavy objects duringuserof avoide for 'thefreason that-the same 'would' become miele4 lyfalnd s asily'daxnaged-froni-slight impacts, requiringeither constant repair or replacement, or' operation under Vdefecselves, but cause undue wear in the shaft.

- Y 4 4. In a direct drive rotary power lawn mower as set forth in claim 3 wherein said guard has an opening therein to permit access to the crank case drain plug of the lawn mower engine.

l5. In a direct drive rotary `power lawn` mower,a platform upon which ,anengine ismounted, an engine drive shaft extending downwardly'thrpugh an opening in said 'tive conditions to theultimate'damage of the entireassinblyx' Furthermore, attempt Yto brace orsupport the Having thus described the inventionv what is claimed Y as new'andedesired to be secured Yby Letters VPatent'is: 1.V In a direct drive rotary power lawn mower, a platform upon which an engine is mounted, an engine drive shaft extending downwardly through an opening in said platform, `a guard connected 'to said platform and disposed 'therebeneath, said guard having an opening vertically spaced (beneath said platform through which the shaft Y extends, said Vshaft being centrally positioned in the guard opening out of contact with the periphery of said opening and adapted to support a cutter blade beneath theV guard, 'the kclearance at the point between the shaft and the periphery of 'theguard opening permitting lateral shaft deflection within the limit` of resilient shaft lexure.

'2'5 ZE'Inadirectl drive rotary power lawn mower, a platform upon which an engine is mounted, an engine drive' 4 shaft extending downwardly through anv opening in said platform, aVdish-shaped downwardly extending Yguard plate connected to said platform and disposed therebeneath,Y

Yadapted to support a cutter blade beneath the guard, the

clearance at the point between the'shaft andthe periphery of theVV guard opening permittingY lateral shaft deflection Vwithin the limit of resilientshaft flexure.

3.511; a direct drive rotary power lawn mower, a platform upon which an engine is mounted,'an engine drive` yfshaftjextending.downwardly through an opening in said platform, .a substantiallyl frusto-conical downwardly exn-V tending'guard plate having its base attached to. said plat- `'forni and disposed therebeneath, said guard having a vcirguard, =said shaft extending through said guard opening 'cular Vopening, in the lowermost and central portion of said 150 Y' y and concentrically positioned with respect theretoout of f contact with the periphery of said opening, said shaft Vadapted `to support a cutter blade beneath the guard, the

clearance at the point between the shaft and the periphery of the guard opening permitting lateral shaft decction Within the limit of resilient shaft lexure. Y

n platform, a guardv conncctedrto said platform and disn posed therebeneath, said-guard `having an annular portion withv an openingrtherein and a lsupport,intcgrfal therewith,

said Svpprt bein'g'eftah'edffweid iilfforh Said @Perline being vertically spaced beneathfthe platform, ,said shaft extending through said opening out `of contact with the periphery of said opening and being Vlcentrally'positioned with respect thereto, said shaft adapted Vto support a cutter blade beneath the guard,l the clearance at the point between the shaft and the periphery of the guard opening permitting lateral shaft deflection within Ythe limit of resilient shaft exure. l,

6. In a direct drive rotary power lawn mower, a platform upon whicn an engine is mounted, anV engine drive shaft, extending downwardly through an opening in said platform, a downwardly extending guard plate connected to said platform and disposed therebeneath, said guard having an opening vertically spaced beneath Vsaid platform through which the'shaft extends, said shaft being centrally positioned in the guard opening out of contact with Vto and not exceeding'the normal resilient shaft ilexure.

7. In a direct vdrive rotary vpower 'lawn mower, a platform upon whichl an engine is mounted, an engine drive shaft extending `downwardlythrough an opening in said platform, av guard connectedrto said platform and dis posed therebeneath, said guard having an lopening vertically spacedV beneath'said platform throughr which the shaft extends, said shaft being centrally positioned in the guard opening out of'contact with theperiphery of said opening andadapted to support a cutter bladebeneath the guard, rthe clearance atY the pointbetweenthe shaft and the periphery of the guard'opening permitting lateral shaft deflection between the lowermostshaft 'bearing and the guard opening -but restricting such deliection sot'hat the limit ofresilientshaft flexure is 'not exceeded.' Y

RefereneesCited in thelile of this patent v UNITED sTArEs rArenr's; L

V1,622,611 .A seral e 2,675,662 Kroll Ap1j.120, 1954 2,680,339 Murphy June 8, 1954 2,720,742 Hilton, Oct. 18, 1955 2,737,003 -Beersgg 4Mar.,6, 1956 2,815,634 YBush -a Dec. 10,1957

Langenbacher. vMay 27, 

